The elbow is a hinge joint that joins the upper arm with the forearm. It is the second link in a mechanical chain of levers that begins at the shoulder and ends at the fingertips The motion of the elbow allows the height and length of the upper extremity to be adjusted, and forearm motion allows the hand to be placed in the most effective position for function. This paper will look at the structure of the elbow and how it functions in various movements, such as the bench press.
The elbow is part of a kinematic chain of joints which runs from the thoracic wall to the fingertips (Smith, Weiss & Lehmkuhl, 1996, pp. 9-10). In this chain, 19 degrees of freedom in planar motions can be identified. This freedom of motion constitutes the mechanical basis for performances of skilled manual activities and the versatility of the upper extremity. Since the elbow contains both convex and concave surfaces on each articulating bone, it is known as a sellar (or saddle) joint. This type of joint permits a large range of motion with an economy of articular surface and reduction in the size of the joint. The unique positioning and interaction of the bones of the elbow joint allow for rotation as well as hinge action.
The bones which form the elbow are the trochlear of the humerus, which sits into the greater sigmoid cavity of the ulna, and allows the movements particular to the elbow joint, i.e. flexion and extension; the lesser, or radial, head of the humerus, which articulates with the cup-shaped depression on the head of the radius; and the circumference of the head of the radius, which articulates with the lesser sigmoid cavity of the ulna, allowing the movements of rotation of the radius and ulna (pronation and supination). The articular surfaces are covered with a thin layer of cartilage, and connected together by a capsular ligament of unequal thickness, being especially thickened on its two sides and, to a lesser extent, in fr...